Research labs are constantly performing experiments with dangerous materials like anti-matter and black holes. Also, they usually have massive power generators providing power to the rest of the lab, the type that can cause wide-spread disaster should they ever go critical.
With all this and more going on in research labs, it's not surprising that the occasional experiment or generator can go awry, causing a massive explosion that destroys the lab and most of the land around it. And then you have the possibility that it wasn't an accident at all...